To buy off the shelf? I don't know (and haven't heard of any) but many of us HTPC owners have such a set-up though.
As for channels only on Freeview, I can think of C4 HD, Dave, Dave ja vu, Five USA, Fiver, Virgin1, Quest, Sky 3, Sky Sports News, and Sky News. Maybe STV HD too, but you can tune into it on satellite.
I see, thanks for the reply, do you know which channels Freesat does not have that freeview does? as I have freeview built in to my TV, but want BBC and ITV HD channels via freesat and would rather use that as my main instead of always changing sources.